Yes you can use alcohol stoves indoors as well as butane stoves.
Even those portable propane fueled stoves can be safely used indoors as long as you allow some ventilation it will be just fine.
It will be no more dangerous than using your natural gas or propane fueled cook stove indoors.
Using a butane stove indoors can be done safely as long as you use proper ventilation procedures.
Just make sure you use the butane stove indoors while having a window cracked open and it will be fine.
During a power outage during a winter ice storm I used a butane cook stove inside my kitchen and set it on top of my electric stove.
That way the range hood could vent the butane fumes outdoors.
If you don't have proper ventilation above or near the butane stove then dangerous fumes could build up inside the house.
But as long as you use the butane stove indoors with ventilation it will be just fine.